phosphate problem

[KLN]

My other water parameters are fine: ammonia - 0; nitrite - o; nitrate - 0; Ca - 370 and coming up slowly with cc additions, etc.
But phosphates remain at .1 to .25 -- it is hard to read the Salifert scale. I have plenty of green macroalgae growing, and harvest it weekly. I only feed the maroon clown and flame angel what they gobble up in a minute or two, and have shrimp, crabs, snails, a starfish and an urchin to clean up.

I have two hob filters running with lots of carbon, and clean the filters a couple of times a week. Aqua C Remora skimmer is working well.

How can I get phosphates to zero?

Thanks.

[jackdp]

Are you using tapwater for top offs or water changes? If you are, then that is probably the culprit. Look for a source of RO water and check it to be sure that it is phosphate free. Also, check your freshly mixed SW just to make sure you are not introducing any PO4 through your salt mix. Double check that you are using high quality carbon and changing it at least every 3 or 4 weeks, lower grade GAC has been known to leech PO4 into the water. HTH